1. Field of the Invention
This invention relates to a multilayer analytical element. More particularly, this invention relates to a multilayer analytical element containing a color indicator system and a peroxidase for detection of hydrogen peroxide which is appropriately employable in quantitative analysis of hydrogen peroxide in a liquid sample, or in quantitative analysis of a specific component through quantitative determination of the amount of hydrogen peroxide produced upon contact of the specific component with an oxidase enzyme system.
2. Description of Prior Arts
A quantitative analysis of a specific component (referred to herein as "analyte") based on quantitative determination of the amount of H.sub.2 O.sub.2 produced by an oxidation reaction between the analyte or a reaction product of the analyte and an oxidase enzyme, by means of an appropriate determination procedure has recently become more important. The reason is that the quantitative determination of H.sub.2 O.sub.2 can be done accurately and reliably, for instance, by photometric determination of a colored product formed by the action of H.sub.2 O.sub.2 in the presence of peroxidase.
As for the photometric determination method based on the above-mentioned principle, there is known a method using a reagent system proposed by P. Trinder (See Ann. Clin. Biochem., 6, 24-27 (1969)). This method involves: producing H.sub.2 O.sub.2 by a reaction between an analyte and an oxidase; causing an oxidative coupling reaction between 4-aminoantipyrine (or an analogue thereof) and a phenol (or a naphthol) in the presence of H.sub.2 O.sub.2 and a peroxidase to produce a colored product; and quantitatively determining the so produced colored product. This reaction system is advantageous because the same detection system is employable regardless of varying the kind of oxidase. Accordingly, this reaction system has been studied for application in detection of various analytes. Examples of analytes particularly important in the art of clinical chemical tests include glucose oxidase, cholesterol oxidase, uricase, glycerol oxidase, and phosphoglucose oxidase.
An analytical element employing said oxidase and a detection system for the produced H.sub.2 O.sub.2 in the form of an integral multilayer analytical element or a strip (such as a filter paper strip) impregnated with these reagents is widely employed for clinical tests. This analytical element comprises a composition containing reagents directly participating in the detection of an analyte which is impregnated in a filter paper strip or the like or coated over a filmy support.
As one example of the multilayer analytical elements containing a color indicator system and a peroxidase, there can be mentioned a multilayer analytical element for quantitative analysis of glucose containing glucose oxidase, peroxidase, 1,7-dihydroxynaphthalene and 4-aminoantipyrine disclosed in U.S. Pat. No. 4,292,272.
The present inventors have studied a multilayer analytical element formulated according to the above-mentioned system and noted that the optical density of color formed in the reagent layer is reduced in the case of using a hemolytic whole blood or hemolytic plasma as a liquid sample, as compared with the case of using a non-hemolytic whole blood or non-hemolytic plasma as the liquid sample. Further noted was that the observed glucose concentration in the former case is lowered than that in the latter case. Upon further studies on this problem, the present inventors have found that this problem is assumed to arise from interference by catalase or substances having a catalase activity contained in the blood.
Accordingly, the present inventors have earnestly continued their studies for elimination of the above-mentioned interference and discovered that the interference by catalase or substances having a catalase activity contained in a blood occurring in a multilayer analytical element for quantitative analysis of glucose is eliminated by incorporating a water-soluble monocarboxylic acid or a salt thereof such as acetic acid or sodium acetate into a constitutional layer such as a layer containing glucose oxidase or a reagent layer containing peroxidase, whereby the color formation efficiency therein is increased and further the reaction rate of a series of the reactions concerned is enhanced. The present invention has been completed upon the discovery.